Abstract

Non-invasive detection methods for tracking gun-launched projectiles are important not only for assessment of gun performance but are also essential for timing a variety of diagnostics, for example, to investigate plate-impact events for shock compression experiments. Measurement of the time of passage of a projectile moving inside of the gun barrel can be achieved by detection of the transient hoop strain induced in the barrel of a light-gas gun by the passage of the projectile using external, barrel surface-mounted optical fiber-Bragg grating strain gauges. Optical fiber-Bragg gratings have been implemented and their response characterized on single-stage and two-stage light gas guns routinely used for dynamic experimentation at Los Alamos National Laboratory. Two approaches, using either broadband or narrowband illumination, were used to monitor changes in the Bragg wavelength of the fiber-Bragg gratings. The second approach, using narrowband laser illumination, offered the highest sensitivity. The feasibility of using these techniques to generate early, pre-event signals useful for triggering high-latency diagnostics was demonstrated.

Received 22 October 2012Accepted 12 February 2013Published online 04 March 2013

Acknowledgments:

Los Alamos National Laboratory is operated by LANS LLC for DOE and NNSA. Funding for this work was provided by LANL Laboratory Directed Research and Development Project 2011012DR, and DOE/NNSA Campaign 2 funds at LANL and NSTec. We gratefully acknowledge the Chamber 9 gas gun team and Kyle Ramos for help with the experiments, and Rick Gustavsen for the gun code calculations used to guide the placement of hoop strain sensors on the launch tube of the two-stage gun. LA-UR-12-25673, approved for public release, distribution is unlimited.